Sound attenuator



INVENTOR ATTORNEYS April 16, 1968 w. H. WELTY SOUND ATTENUATOR 5SheedS-Sheet 1 Filed Oct. 18, 1965 W/LL/AM H. WELT) BY MWMWM 77w MfmwiApril 16, 1968 w. H. WELTY SOUND ATTENUATOR 5 Sheets-Sheet 2 Filed Oct.18, 1965 INVENTOR WILLIAM H. WELT) WW ATTOgNEYS April 16, 1968 w. H.WELTY 3,378,100

SOUND ATTENUATOR Filed Oct. 18, 1965 3 Sheets-Sheet l5 5 INVENTORWILL/AM H. WELT) BY W%m7/M,

ATTORNEY5 United States Patent 3,378,100 SOUND ATTENUATOR William H.Welty, Brookfield, Wis., assignor to Air Filter Corporation, Milwaukee,Wis., 'a corporation of Wisconsin Filed Oct. 18, 1965, Ser. No. 497,06115 Claims. (Cl. 181--56) ABSTRACT OF THE DISCLOSURE A sound attenuatingdevice having a plurality of sound absorbing bafiies arranged instaggered, spaced apart relation in a plurality of rows extendingtransversely of air flowing through the device. Each baffle is formed bya metal frame having a relatively rigid panel sandwiched between tworectangularly shaped panels of acoustically absorbent material. Theacoustically absorbent panels are mounted in back-to-back relation onthe frame and are each cambered away from the frame panel to define amultiplicity of smoothly curved air flow orifices.

This invention relates to sound attenuators and is particularlyconcerned with silencing structures for absorbing sound accompanying theflow of a fluid medium such as air in a confined space.

The movement of air through confining ducts, conduits, grilles, or otherstructures, as is required, for instance, in air conditioning,ventilating, and heating systems, is frequently accompanied byobjectionable noises which may initiate from the operation of equipmentor from other sources. Prior to this invention, it has been the practiceto isolate a room or other space from these noises by providingacoustical silencers or so-called sound traps of varying constructionsfor absorbing the sounds being transmitted with the air stream.Conventional silencers employed for this purpose generally areineffective in low frequencies to reduce objectionable noise to anacceptable level and/or offer undesirably high resistance to air flow.Increasing the noise suppression efficiency of conventional soundabsorbing devices usually is accompanied by a correspondingobjectionable increase in resistance to air flow to cause an excessivepressure drop, for example, in an air duct or conduit system.

It is a primary object of this invention to overcome thef oregoingshortcomings of conventional sound absorbing structures by providing fora novel sound attenuating device which obtains maximum attenuation withminimum resistance to fluid flow.

In fulfilling the foregoing object, the sound attenuating device of thisinvention is provided with a plurality of specially formed soundabsorbing baffles arranged in staggered spaced apart relation in aplurality of rows extending transversely of the air stream and havingsound opaque surfaces gradually cambered or lofted in a direction facingair flow to define a multiplicity of smoothly curved air flow orificeswhich are shaped in the form of bellmouths. This construction, inaddition to affording an exceptionally high reduction in the noiselevel, minimizes friction and turbulence resisting air flow tocorrespondingly minimize the fluid pressure drop across the soundattenuating structure.

Another important object of this invention is to provide a novel soundattenuating device which is compact in construction and which isnon-directional to both sound and air flow, providing the same highlyetlicient noise reduction performance and the same low resistanceregardless of the direction of fluid flow.

As a result, the sound attenuating device of this invention may readilybe located between transfer grilles providing fluid communication, forexample, between a room and a corridor or another room to cut down noisetransfer and cross-talk. By constructing the sound attenuator of thisinvention as a compact unit, it may easily be located in ducts behindsupply or return grilles or in plenum chambers to minimize the noiseentering an airconditioned, heated, or ventilated space.

Still another object of this invention is to provide a novel, compactsound attenuating unit which is simple and inexpensive to manufactureand which is easy to install.

Further objects of this invention will appear as the descriptionproceeds in connection with the appended claims and the annexed drawingswherein:

FIGURE 1 is a sectional View illustrating the sound attenuating deviceof this invention mounted between opposed air transfer grilles;

FIGURE 2 is a front elevation of the sound attenuating device shown inFIGURE 1;

FIGURE 3 is a left hand end elevation of the sound attenuating deviceshown in FIGURE 2;

FIGURE 4 is a section taken substantially along lines 4-4 of FIGURE 2;

FIGURE 5 is an end elevation of one of the main sound absorbing,baffling modules shown in FIGURES 2 and 4;

FIGURE 6 is an end elevation of another of the sound absorbing, battlingmodules illustrated in FIGURES 2 and 4;

FIGURE 7 is a sectional view illustrating the sound attenuating deviceof FIGURE 2 mounted behind a return air grille in a ventilating,heating, or air conditioning system; and

FIGURE 8 is a sectional view illustrating the sound attenuating deviceof FIGURE 2 mounted behind a return ceiling grille in an airconditioning, heating, or ven tilating system.

Referring now to the drawings and more particularly to FIGURE 1, thereference numeral 10 generally designates a sound attenuator constructedaccording to a preferred embodiment of this invention and shown to bemounted in a straight air flow passage 12 between tWo opposed airtransfer grilles 14 and 16 of conventional form. Passage 12 may beformed in a wall 18 or other partition separating, for example, tworooms or a room and corridor to provide for the bi-directional transferof air between the spaces separated by wall 18. Passage 12 may bestraight and rectangular in cross-section to accommodate grilles 14 and16.

As best shown in FIGURES 2 and 3, attenuator 10 comprises a rigid,metallic support frame 20 having flatsided parallel transverse plates 22and 24 rigidly joined together by parallel, fiat-sided side plates 26and 28 to form a rectangular frame construction. Frame 20 may be fixedin arfy suitable manner in passage 12 with plates 22, 24, 26, and 28butting against related wall surfaces of passage 12 so that all of theair flowing in either direction through passage 12 passes through frame20.

Referring to FIGURES 2 and 4, attenuator 10 is provided with a pluralityof sound absorbing baflling units or modules 30 which extend in parallelrelation across the entire width of frame 20 between side plates 26 and28 and which are fixed to frame 20 in a manner to be described later on.Modules 30 are symmetrical about normally intersecting longitudinal andtransverse planes and are arranged in two parallel, spaced apart,straight rows 32 and 34 extending essentially at right angles to themovement of air flow through passage 12. Row 32 is formed entirely ofmodules 30 which are uniformly spaced apart and extend transversely ofthe movement of air in either direction through passage 12. Row 34contains a plurality of modules 30 and a further pair of soundabsorbing, bafiiing units or modules 36. Modules 36 essentially aretransverse half sections of modules 30 and are disposed at opposite endsof row 34. As shown, modules 36 extend the entire Width of frame inparallel uniformly spaced apart relation to the adjacently disposedmodules and are fixed to frame 20 by means to be described shortly.

The modules in row 34 are uniformly staggered with respect to themodules in row 32. This staggered spacing of modules 30 and 32 in theirrespective rows is such that a module 30 in one row is in overlappingrelation with adjacently disposed modules in the other row to define asolid rectangular figure. With this arrangement, air flowing along astraight line in either direction will impinge against at least one ofthe modules 30, 36 in either row 32 or row 34.

With continued reference to FIGURE 4, modules 30 and 36 each are formedwith opposite facing, gradually and uniformly cambered acousticallyopaque surfaces 38 and 40. Surfaces 38 on the modules 30 in row 32 arelofted or combered toward air flow entering the right side of theattenuator, and surfaces 38 on the modules 30 and 36 are lofted towardair flow entering the left side of attenuator 10. Surfaces 40 on themodules in rows 32 and 34 respectively are in opposed relation as shown.Surfaces 38 on adjacently disposed modules in row 32 define a pluralityof uniformly spaced apart, equally dimensioned, bellmouthed orifices 42.Similarly, surfaces 38 on the modules in row 34 define a plurality ofuniformly spaced apart, bellmouthed orifices 43 having the samedimensions as orifices 42. Orifices 42 and 43 respectively converge inopposite directions toward throat sections of reduced fluid flow area.Surfaces 40 on adjacently disposed modules in each row define opposedbellmouthed orifices 42a and 43a which flare outwardly from the throatsections of orifices 42 and 43 toward the space between rows 32 and 34.Each aligned pair of orifices 43 and 43a in row 34 and each aligned pairof orifices 42 and 42a in row 32 thus forms a venturi passage throughwhich air in passage 12 is adapted to flow.

Each of the modules 30, as best shown in FIGURE 5, comprises a mountingframe 46 and a pair of relatively thick, solid, rectangular, flat-sidedpanels 48 and 50 made of any suitable acoustically absorbent materialsuch as, for example, long strand fibre glass preferably having adensity of about four pounds per cubic foot. Preferably, panels 48 and50 are of uniform thickness and are flexible and deformable. Panels 48and 50 are faced with a covering indicated at 51 to define surfaces 38and 40. Covering 51 may be made of any suitable material.

Frame 46 comprises a pair of separately formed, fiat sided sections 52and 54 respectively mounting panels 48 and 50 and made of sheet metal orother suitable material. The upper and lower marginal edges of section52 are sharply bent laterally outwardly at right angles from anintermediate, substantially straight body portion 56 to define a pair oflips 58 and 60. Lips 58 and 60 are smoothly curved backwardly towardeach other to form oppositely facing rounded corners at opposite ends ofbody portion 56. As shown, lips 58 and 60 respectively form with bodyportion 56 opposed, open ended, parallel grooves 62 and 64 each having acurved bottom wall surface normally intersecting with a straight sidewall surface defined by body portion 56 and smoothly merging with anoutwardly curved side wall surface defined by the lip end.

Section 54 is of the same construction as section 52. Accordingly likereference numerals have been used to identify like elements.

Still referring to FIGURE 5, sections 52 and 54 are rigidly joinedtogether by any suitable means in back-toback relationship with the bodyportions 56 of sections 52 and 54 butted along an interface containingin a longitudinal plane which medially intersects module 38.

With reference to FIGURES 3 and 5, body portions 56 of sections 52 and54 are wedged apart to define tapered holes 66 at opposite ends of frame46. Suitable sheet metal or like screws 68 extending through side walls4 26 and 28 are threaded into holes 66 to removably, rigidly mount frame46 on frame 20.

As best shown in FIGURE 5, the upper and lower marginal edges of each ofthe panels 48 and 50 is slidably received in grooves 62 and 64. Lips 58and 60 snugly clamp and compress the marginal edges of each panel, thuscausing each panel to bow uniformly outwardly so that the central bodyportion of each panel extending between lips 58 and 60 is spacedforwardly from the body portions 56 of mounting frame 46. By thissimplified clamping arrangement panels 48 and 50 are supported inback-to-back relation on mounting frame 46 and are provided withuniformly lofted or air-foil cross sections which camber in oppositedirections.

In the assembly of attenuator 10, modules 30 are first assembled bysliding panels 48 and 50 endwise into their associated pair of grooves62 and 64 on frame sections 52 and 54. Modules 30 thus assembled aremounted in frame 20 in the manner already described. If it is desired toreplace panels 48 and 50, modules 30 are removed from frame 20, the oldpanels slid out of grooves 62 and 64, and new panels inserted in theirplace.

Referring now to FIGURE 6, the module 36 at each end of row 34 comprisesa mounting frame 70 for supporting a pair of flat-sided, solid,rectangular panels 72 and 74 each having uniform thickness andpreferably made of the same material as panels 48 and 50. Frame 70comprises a pair of separately formed, flat-sided sections 76 and 78respectively mounting panels 72 and 74 and made of sheet metal or othersuitable material.

With continued reference to FIGURE 6, section 76 is bent at its upperend to provide an outwardly extending portion 80 normally intersectingan upstanding body portion 82. The outer marginal end of portion 80 isbent downwardly to form a flange portion 84 which is in parallelrelation to body portion 82. The lower end of body portion 82 is sharplybent outwardly to form a lip 86 which is smoothly curved forwardly andupwardly to provide a rounded corner. Lip 86 and body portion 82 definean open-ended groove 88 similar to grooves 62 and 64 in modules 30.

The lower end of panel 72 is slidably received in groove 88 and isclamped and compressed between opposed surfaces on lip 86 and bodyportion 82. The upper end of panel 72 is slidably received in anopen-ended groove defined by flange portion 84 and body portion 82. Asshown, flange portion 84 is spaced laterally outwardly from lip 86, andthe lateral dimension between flange portion 84 and body portion 82 isappreciably greater than the thickness of panel 72. Thus, by clampinglyengaging and compressing the lower end of panel 72 between lip 86 andbody portion 82, the upper end of panel 72 being resilient and flexibleis sprung or bowed outwardly to engage flange portion 84 so that thecontour of its outer surface is lofted in the form of a half camberhaving a crest disposed adjacent flange 84 and being smoothly bowed backto the clamped end at lip 86.

Frame section 78 is of the same construction as section 76. Accordingly,like reference numerals have been used to identify like portions. Panel74 is mounted on frame section 78 in the same manner as panel 72 ismounted on section 76.

The body portions 84 of frame sections 76 and 78 are rigidly fixedtogether in back-to-back relation by spot welding or any other suitablemeans. Sections 76 and 78 are thus .joined along aninterface whichmedially intersects module 36. Body portions 84 of sections 7 6 and 78are wedged apart to define opposite opening, tapered holes 96. Suitablesheet metal screws 92 extending through side walls 26 and 28 arethreaded into holes 90 to removably, rigidly secure mounting frame 70 toframe 20. In the assembled position of parts, portions 80 of mountingframe 70 butt against frame 20.

From the foregoing description, it will be appreciated thatair flowingfrom right to left through passage 12 in FIGURE 1 passes seriallythrough orifices 42, 42a, 43a, and 43 and will impinge against at leastone of the modules 30, 36 in rows 32 and 34. The sound energyaccompanying air that impinges against modules 30 in row 32 will readilybe absorbed by the cambered panels defining surfaces 38 which direct theimpinging air to flow smoothly into orifices 42 without producingturbulence. The confined, dead air spaces between panel 48 and framesection 52 and between panel 50 and frame section 54 in each moduleserve to minimize the transmission of sound produced vibrations throughthe module itself. Similar dead air spaces are provided in modules 36.

The air channeled through orifices 42 pass smoothly through orifices 42awhich allow the air stream to gradually diverge and impinge in auniformly distributed pattern against surfaces 40 on the modules in row32 to further reduce the noise level. Surfaces 40, being uniformlycambered, smoothly direct the air into orifices 42a which channels theair stream without turbulence into orifices 43. Orifices 43 graduallyallow the air streams to-diverge again for continued flow throughpassage 12. Thus, the arrangement and construction of modules 30 and36jin rows 32 and 34 and the related contours of orifices 42, 42a, 43and 43a provides for maximum attenuation ofsound with least resistanceto air flow and with negligible air turbulence.

Since each of the modules 30 and 36 is symmetrical and ,since therelated dimensions of bellmouthed orifices and modules in rows 32 and 34are the same, it will be appreciated that attenuator provides for thesame highly effective noise reduction and the same low resistance to airflowing in either direction through passage 12. Air moving from left toright in FIGURE 1 will serially pass through orifices 43, 43a, 42a, and42 in the same manner as just described for air flowing in the oppositedirection. This aspect of the invention and the compact, slimconstruction of attenuator 10 thus enables attenuator 10 to easily belocated in a straight passage between opposed air transfer grilles asshown in FIGURE 1. In addition to being simple and inexpensive tomanufacture, the attenuator device of this invention is easy to installin any desired location, as shown, for example in FIGURES l, 7, and 8.Experiments have shown that the attenuator of this invention isinstrumentally effective in all bands and cuts sound energy in half withevery three decibel reduction.

As shown in FIGURE 7, attenuator 10 is readily and easily mounted behindair supply grille 100 in a rectangular passage 102 which is formed in awall 104. A duct 106 is shown connected to passage 102 to convey airthrough grille 100.

' In FIGURE 8, attenuator 10 is shown to be mounted behind an air returngrille 110 in a rectangular opening 112 which is formeciin a suspendedceiling 114. Air enters the space below ceiling 114 through a duct 116and is drawn through grille 110 and then through attenuator 10 into theconfined space above ceiling 114.

The invention may be embodied in other specific forms without departingfrom the spirit or essential characteristics thereof. The presentembodiment is therefore to he considered in all respects as illustrativeand not restrictive, the scope of the invention being indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are therefore intended to be embraced therein.

What is claimed and desired to be secured by Letters Patent is:

1. A sound attenuator for absorbing sound energy accompanying flow ofgases and comprising a frame delimiting a passage through which saidgases are adapted to fiow, a plurality of first baflling units mountedon said frame in uniformly spaced apart relation extending across saidpassage and arranged in a straight row extending transversely of gasflow through the space delimited by said frame, and a plurality ofsecond bafiling units mounted on said frame and extending across saidpassage in parallel relation to said first baffling units, said secondbafiling units being arranged in a second row extending rearwardly ofand in parallel, spaced apart relation to said first row, said first andsecond baffling units having panels of sound absorbing materialextending across said passage and being uniformly cambered in paralleldirections facing flow of gas through said passage, the cambers on thepanels of adjacently disposed baflling units in each row definingbellmout'hed orifices each converging in the direction of gas flowtoward a throat section of reduced flow area, said second bafiling unitsbeing staggered relative to said first baflling units and eachoverlapping adjacently disposed baffling units in said first row toextend across the path of the gases flowing through the bellm-outhedorifices in said first row, each of said baffiing units comprising apanel support frame structure and each of said panels being formed ofresilient, flexible material, said support frame structure being for-medwith a pair of fl-ange sections rigidly joined to gether by anintermediate section and defining therewith opposed, spaced apart, openended grooves slidably receiving opposite marginal edges of itsassociated panel, at least one of said flange sections clampinglyengaging and compressing the panel against said intermediate section tooutwardly bow the portion of the panel extending between said flangesections.

2. A sound attenuator for absorbing sound energy accompanying flow ofgases and comprising a frame delimiting a passage through which saidgases are adapted to flow, a plurality of first baffling units mountedon said frame in uniformly spaced apart relation extending across saidpassage and arranged in a straight row extending transversely of gasflow through the space delimited by said frame, and a plurality ofsecond baffling units mounted on said frame and extending across saidpassage in parallel relation to said first baflling units, said secondbaffling units being arranged in a second row extending rearwardly ofand in parallel, spaced apart relation to said first row, said first andsecond bafliing units having panels of sound absorbing materialextending across said passage and being uniformly cambered in paralleldirections facing flow of gas through said passage, the cambers on thepanels of adjacently disposed bafiling units in each row definingbellmouthed orifices each converging in the direction of .gas flowtoward a throat section of reduced flow area, said second baflling unitsbeing staggered relative to said first baffling units and eachoverlapping adjacently disposed baffling units in said first row toextend across the path of the gases flowing through the bellmouthedorifices in said first row, at least one of said baffling units at leastin said second row comprising a panel support frame, and at least one ofthe panels of said one unit being made of resilient, flexible material,said support frame being formed with a body section having oppositemarginal ends bent forwardly and toward each other to define opposed,spaced apart, open ended grooves sl-idably receiving opposite marginaledges of said one panel, each marginal edge of said one panel beingcompressed between opposed internal surfaces defining each groove to howthe portion of the panel between sa-id grooves outwardly from saidsupport frame.

3. A sound attenuator for absorbing sound energy accompanying flow ofgases and comprising a frame delimiting a passage through which thegases are adapted to flow, a plurality of first bafliin-g unit's mountedon said frame in uniformly spaced apart relationship extending acrosssaid passage between opposed side portions of said frame, said firstbafliing units being arranged in a straight row extending transverselyof gas fiow through said passage, and a plurality of second bafliingunits mounted on said frame and extending across said passage inparallel relation to said first baffling units, said second balfiingunits being arranged in a straight row extending in parallel spacedapart, side-byaside relationship to the row containing said firstbafiiing units, each of said first and second bafliing units beingsymmetrical about a plane extending parallel to said rows and having apair of sound absorbing panels extending across said passage and beingcambered in opposite directions respectively facing gas flow in oppositedirections through said passage, the cambers of the panels on adjacentlydisposed baffling units in each row defining a venturi passageterminating at opposite ends in oppositely flared bellmouths, thebaflling units in one row being staggered relative to the baffling unitsin the other of said rows and each overlapping adjacently disposed unitsin the other row in spaced relation to the venturi passages therein tothereby extend across the path of gases flowing through the venturipassages in the other row, at least one baflling unit in each rowcomprising a panel support frame structure extending across saidpassage, and said panels being formed from resilient flexible material,said support frame structure being formed by a pair of plates mountingrespective ones of the two panels in the unit and being fixed togetherin back-to-back relation, each of said plates having opposite marginalend portions bent forwardly and toward each other to define opposed,spaced apart open ended grooves slidably, removably receiving oppositemarginal edges of its associated panel, the width of each groove beingso dimensioned as to clampingly compress the associated marginal edge ofthe panel between opposed groove surfaces to how the portion of thepanel extending between the opposed pair of grooves outwardly from theportion of the plate extending between said bent ends.

4. A sound attenuator for absorbing sound energy accompanying flow ofgases through a confined space and comprising a plurality of bafliingmodules staggeringly arranged in a plurality of side-by-side spacedapart rows extending transversely of the direction of gas flow, each ofsaid modules comprising a pair of panels formed from defiormable,acoustically absorbent material and with oppositely facing sidesurfaces, and a relatively rigid frame mounting said panels inback-to-back relation transversely of the gas fl-ow through said spaceand with the side sur faces of said panels which face away from eachother respectively confronting and being impinged by gas flowing fromopposite directions, said frame being formed with a panel-like sectionsandwiched between and separating said panels, said section extendingtransversely of gas flow in either direction through said space, andsaid frame being further formed with means extending from said sectionand overlapping the transversely extending marginal edges of each of thepanel side surfaces confronting gas flow to engage and confine saidpanels against said section.

5. The sound attenuator define-d in claim 4 wherein said firame isformed by a pair of separately formed members having rectangular, fl-atsided portions fixed in abutting, back-to back relation to define saidsection, and wherein said means extending from said section comprises apair of lips formed integral with each of said rectangular portions.

6. The sound attenuator defined in claim 4 wherein said means extendingfrom said section comprises a pair of lips for each of said panels, eachlip cooperating with said section to define a transverse groovereceiving one of the marginal edges of an associated panel.

'7. The sound attenuator defined in claim 6 wherein each of said panelsare slidably received in their associated grooves and wherein thegrooves associated with each panel are open at least at correspondingends to provide for the endwise removal of each panel from said frame.

8. The sound attenuator defined in claim 4 wherein adjacent ones of saidmodules in each row define a bellmouthed orifice converging in thedirection of gas flow from a relatively wide, outwardly flared entranceopening toward a throat region of reduced flow area.

9. The sound attenuator defined in claim 4 wherein each of said panelsis bowed away from said section to form between adjacent modules in eachrow a bellmouthed orifice converging in the direction of gas flow fromarelatively wide, outwardly flared entrance opening toward a throatregion of reduced flow area.

10. A sound attenuator for absorbing sound energy accompanying flow ofgases through a confined space and comprising a plurality of bafliingmodules staggeringly arranged in a plurality of side by-side spacedapart rows extending transversely of the direction of gas flow throughsaid space, each of said modules comprising a pair of separately formedpanels of acoustically absorbent material and a relatively rigid framemounting said panels in back-to-back relation transversely of the gasflow through said space and having a panel-like section sandwichedbetween and separating said panels, said panels having side surfacesfacing away from said section and impinged by gas flowing from oppositedirections, said frame including means extending from said section andover lapping only peripheral portions of said side surfaces to retainsaid panels in said backt-o-back relation.

11. The sound attenuator defined in claim 10 wherein said panels aresymmetrically disposed on opposite sides of a plane mediallyintersecting the associated baflling unit.

12. The sound attenuator defined in claim 10 wherein said meansextending from said section comprises a pair of lips for each of saidpanels and extending over opposite edges of each panel, said lipscooperating with said sect-ion to define spaces receiving and confiningsaid opposite edges,

13. The sound attenuator defined in claim 12 wherein said section is ofsubstantially rectangular configuration and wherein said pair of lips.are bent toward each other and terminate in spaced apart relation, thepanel associated with each pair of lip-s being continuous in the regionbetween the ends of said lips.

14. The sound attenuator defined in claim 12 comprising a structuresupporting said modules and having spaced apart portions, said modulesextending between said portions of said structure, and said frame beingfixed at opposite ends to said portions of said structure, said lipsextending transversely between said port-ions of said structure anddelimiting passages providing for the flow of the gas around saidmodules.-

15. The sound attenuator defined in claim 10 wherein said meansextending from said section delimits passagew ays providing tor thepassage of the gas around said modules.

References Cited UNITED STATES PATENTS 1,865,677 7/ 1932 Cheyney 181-602,656,004 10/1953 Olson 181-33 2,759,554 8/1956 Baruch 181-56 2,916,1011 2/1959 Naman 18'1-46 XR 2,942,682 6/1960 Bergh et al. 181-56 2,959,24311/1960 Smith 181-56 XR FOREIGN PATENTS 638,407 6/1950 Great Britain.721,859 1/ 1955 Great Britain.

ROBERT S. WARD, 111., Primary Examiner.

